[llvm] fd23677 - [IndVars] Forget SCEV for value after simplifying condition.

[Florian Hahn via llvm-commits]

Author: Florian Hahn
Date: 2022-10-21T11:18:01+01:00
New Revision: fd236772f5665ce9e55f85ac992be6c22a918d3e

URL: https://github.com/llvm/llvm-project/commit/fd236772f5665ce9e55f85ac992be6c22a918d3e
DIFF: https://github.com/llvm/llvm-project/commit/fd236772f5665ce9e55f85ac992be6c22a918d3e.diff

LOG: [IndVars] Forget SCEV for value after simplifying condition.

Additional SCEV verification highlighted a case where the cached loop
dispositions where incorrect after simplifying a condition in IndVars
and moving the user in LoopDeletion. Fix it by invalidating ICmp and all
its users.

Fixes #58515.

Added: 
    

Modified: 
    llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
    llvm/test/Transforms/IndVarSimplify/invalidate-modified-lcssa-phi.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp b/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
index 11efcae029579..9e23fa9af786b 100644
--- a/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
@@ -289,6 +289,7 @@ void SimplifyIndvar::eliminateIVComparison(ICmpInst *ICmp,
     Users.push_back(cast<Instruction>(U));
   const Instruction *CtxI = findCommonDominator(Users, *DT);
   if (auto Ev = SE->evaluatePredicateAt(Pred, S, X, CtxI)) {
+    SE->forgetValue(ICmp);
     ICmp->replaceAllUsesWith(ConstantInt::getBool(ICmp->getContext(), *Ev));
     DeadInsts.emplace_back(ICmp);
     LLVM_DEBUG(dbgs() << "INDVARS: Eliminated comparison: " << *ICmp << '\n');

diff  --git a/llvm/test/Transforms/IndVarSimplify/invalidate-modified-lcssa-phi.ll b/llvm/test/Transforms/IndVarSimplify/invalidate-modified-lcssa-phi.ll
index 265a985d0f7fc..fb748ae4dc494 100644
--- a/llvm/test/Transforms/IndVarSimplify/invalidate-modified-lcssa-phi.ll
+++ b/llvm/test/Transforms/IndVarSimplify/invalidate-modified-lcssa-phi.ll
@@ -120,3 +120,39 @@ exit:
   %lcssa = phi i32 [ %0, %loop.2.latch ]
   ret i32 %lcssa
 }
+
+
+define i16 @test_pr58515_invalidate_loop_disposition(ptr %a) {
+; CHECK-LABEL: @test_pr58515_invalidate_loop_disposition(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[SEL:%.*]] = select i1 true, i16 2, i16 0
+; CHECK-NEXT:    br label [[LOOP:%.*]]
+; CHECK:       loop:
+; CHECK-NEXT:    [[IV:%.*]] = phi i16 [ 1, [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[LOOP]] ]
+; CHECK-NEXT:    [[SUM:%.*]] = phi i16 [ 0, [[ENTRY]] ], [ [[SUM_NEXT:%.*]], [[LOOP]] ]
+; CHECK-NEXT:    [[SUM_NEXT]] = add i16 [[SEL]], [[SUM]]
+; CHECK-NEXT:    [[IV_NEXT]] = add nuw nsw i16 [[IV]], 1
+; CHECK-NEXT:    [[C_2:%.*]] = icmp ult i16 [[IV]], 9
+; CHECK-NEXT:    br i1 [[C_2]], label [[LOOP]], label [[EXIT:%.*]]
+; CHECK:       exit:
+; CHECK-NEXT:    [[LCSSA:%.*]] = phi i16 [ [[SUM_NEXT]], [[LOOP]] ]
+; CHECK-NEXT:    ret i16 0
+;
+entry:
+  br label %loop
+
+loop:
+  %iv = phi i16 [ 1, %entry ], [ %iv.next, %loop ]
+  %sum = phi i16 [ 0, %entry ], [ %sum.next, %loop ]
+  %gep = getelementptr inbounds i16, ptr %a, i16 %iv
+  %c.1 = icmp ne ptr %a, %gep
+  %sel = select i1 %c.1, i16 2, i16 0
+  %sum.next = add i16 %sel, %sum
+  %iv.next = add nuw nsw i16 %iv, 1
+  %c.2 = icmp ult i16 %iv, 9
+  br i1 %c.2, label %loop, label %exit
+
+exit:
+  %lcssa = phi i16 [ %sum.next, %loop ]
+  ret i16 0
+}